Volume extent allocation

ABSTRACT

A computer program product for processing an extend request for a data set in a storage facility is disclosed. The computer program product may include receiving the extend request. The extend request may include a new extent allocation amount for the data set. The data set may be associated with a number of volumes in the storage facility. The computer program product may include apportioning the new extent allocation amount among fractional amounts. The computer program product may include allocating the fractional amounts.

TECHNICAL FIELD

This disclosure relates generally to computer-implemented data storageand, more particularly, relates to allocating data sets.

BACKGROUND

The amount of data that needs to be managed by enterprises is growing atan extremely high rate. One challenge facing database management systemsis allocating sufficient storage space to accommodate a data set that isexpanding in size. A customer of a database management service typicallymust review their data set compared to a current allocation to ensurethat sufficient storage space and logical storage units are availablefor an addition to the data set.

SUMMARY

A computer program product for processing an extend request for a dataset in a storage facility is disclosed. The computer program product mayinclude receiving the extend request. The extend request may include anew extent allocation amount for the data set. The data set may beassociated with a number of volumes in the storage facility. Thecomputer program product may include apportioning the new extentallocation amount among fractional amounts. The computer program productmay include allocating the fractional amounts.

Aspects of the disclosure include a computer program product allowingspecific data sets to be able to spread a new extent allocation amountacross multiple volumes. Spreading the new extent allocation amountacross multiple volumes may allow an extend request to succeed and notdisrupt applications. An allocation threshold of a selected StorageGroup (SG) may be altered to a higher value. A failed extend request maybe repeated. If the extend request still fails, the new extendallocation amount may be spread over (up to) a number of candidatevolumes. The number of candidate volumes may be defined in the extendingdata sets catalog entry. In embodiments, the new extend allocationamount may be spread up to a defined Dynamic Volume Count (DVC) for thedata set. If no candidate volumes exist, and the data set is definedwith a DVC, the same methodology of spreading the new extent allocationamount across the DVC may be used. If spreading the new extentallocation amount across multiple volumes succeeds, control may bepassed back to the application and normal processing may continue. Inembodiments, a space management utility may key off a new value. The newvalue may be a new bit. The space management utility may move data offthe multiple volumes to a primary volume for a data set. The multiplevolumes may be returned to a candidate status in a catalog.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example network architecture according to anembodiment;

FIG. 2 illustrates an example storage system containing an array ofstorage devices according to an embodiment;

FIG. 3 is a flowchart illustrating an operation processing an extendrequest according to an embodiment; and

FIG. 4 shows modules of a system implementing an operation according toan embodiment.

DETAILED DESCRIPTION

In available database management solutions a data set may be stored inone or more volumes. In each volume a particular database managementsolution may make allocations known as extents. The maximum number ofvolumes permitted for a data set may be a predetermined value or may beuser specified. When a data set needs to extend to an additional volume,the entire new extent allocation amount must be obtained on a singlevolume within a Storage Group (SG) of devices. In highly activeenvironments these devices can become fully utilized which can prevent aStorage Management Subsystem (SMS) from extending the data set toanother device because no single device in the SG contains enough freespace below its defined allocation threshold to satisfy the request.This can lead to application failures which require the additional spacein the data set to continue input-output (I/O) processing. Aspects ofthe disclosure include a methodology allowing specific data sets to beable to spread the new extent allocation amount across multiple volumes.Spreading the new extent allocation amount across multiple volumes mayallow an extend request to succeed and not disrupt applications.

Aspects of the disclosure may enable data sets to extend to additionalvolumes to avoid disrupting an application. An allocation threshold of aselected SG may be altered to a higher value. A failed extend requestmay be repeated. If the extend request still fails, the new extendallocation amount may be spread over (up to) a number of candidatevolumes. The number of candidate volumes may be defined in the extendingdata sets catalog entry. In embodiments, the new extend allocationamount may be spread up to a defined Dynamic Volume Count (DVC) for thedata set. If no candidate volumes exist, and the data set is definedwith a DVC, the same methodology of spreading the new extent allocationamount across the DVC may be used. If spreading the new extentallocation amount across multiple volumes succeeds, control may bepassed back to the application and normal processing may continue. Inembodiments, a space management utility may key off a new value. The newvalue may be a new bit. The space management utility may move data offthe multiple volumes to a primary volume for a data set. The multiplevolumes may be returned to a candidate status in a catalog.

FIG. 1 illustrates an example network architecture 100 according to anembodiment. The network architecture 100 is presented to show oneexample of an environment where a system and method in accordance withthe disclosure may be implemented. The network architecture 100 ispresented only by way of example and is not intended to be limiting. Thesystem and methods disclosed herein may be applicable to a wide varietyof different computers, servers, storage devices, and networkarchitectures, in addition to the network architecture 100 shown.

As shown, the network architecture 100 includes one or more computers102, 106 interconnected by a network 104. The network 104 may include,for example, a local-area-network (LAN) 104, a wide-area-network (WAN)104, the Internet 104, an intranet 104, or the like. In certainembodiments, the computers 102, 106 may include both client computers102 and server computers 106 (also referred to herein as “host systems”106). In general, client computers 102 may initiate communicationsessions, whereas server computers 106 may wait for requests from theclient computers 102. In certain embodiments, the computers 102 and/orservers 106 may connect to one or more internal or externaldirect-attached storage systems 112 (e.g., arrays of hard-disk drives,solid-state drives, tape drives, etc.). These computers 102, 106 anddirect-attached storage systems 112 may communicate using protocols suchas ATA, SATA, SCSI, SAS, Fibre Channel, or the like. One or more of thestorage systems 112 may contain storage pools that may benefit fromallocation techniques of the disclosure.

The network architecture 100 may, in certain embodiments, include astorage network 108 behind the servers 106, such as astorage-area-network (SAN) 108 or a LAN 108 (e.g., when usingnetwork-attached storage). This network 108 may connect the servers 106to one or more storage systems 110, such as arrays 110 a of hard-diskdrives or solid-state drives, tape libraries 110 b, individual hard-diskdrives 110 c or solid-state drives 110 c, tape drives 110 d, CD-ROMlibraries, or the like. To access a storage system 110, a host system106 may communicate over physical connections from one or more ports onthe host 106 to one or more ports on the storage system 110. Aconnection may be through a switch, fabric, direct connection, or thelike. In certain embodiments, the servers 106 and storage systems 110may communicate using a networking standard such as Fibre Channel (FC).One or more of the storage systems 110 may contain storage pools thatmay benefit from allocation techniques according to the disclosure.

FIG. 2 illustrates an example storage system 110 a containing an arrayof storage devices 204 (e.g., hard-disk drives 204 and/or solid-statedrives 204) according to an embodiment. The internal components of thestorage system 110 a are shown as allocation techniques according to thedisclosure and may be used to allocate data sets for logical volumesresiding within such a storage system 110 a. Nevertheless, allocationtechniques according to the disclosure may also be implemented withinother storage systems 110, 112. As shown, the storage system 110 aincludes a storage controller 200, one or more switches 202, and one ormore storage devices 204, such as hard-disk drives 204 or solid-statedrives 204 (e.g., flash-memory-based drives 204). The storage controller200 may enable one or more hosts 106 (e.g., open system and/or mainframeservers 106) to access data stored in the one or more storage devices204.

As shown in FIG. 2, the storage controller 200 includes one or moreservers 206. The storage controller 200 may also include host adapters208 and device adapters 210 to connect the storage controller 200 tohost devices 106 and storage devices 204, respectively. Multiple servers206 a, 206 b may provide redundancy to ensure that data is alwaysavailable to connected hosts 106. Thus, when one server 206 a fails, theother server 206 b may remain functional to ensure that I/O is able tocontinue between the hosts 106 and the storage devices 204. This processmay be referred to as a “failover.”

Particular enterprise storage systems may have a storage system 110 ahaving an architecture similar to that illustrated in FIG. 2. Particularenterprise storage systems may include a high-performance, high-capacitystorage controller providing disk storage that is designed to supportcontinuous operations. Particular enterprise storage systems may useservers 206 a, 206 b, which may be integrated with a virtualizationengine technology. Nevertheless, allocation techniques according to thedisclosure are not limited to any specific enterprise storage system 110a, but may be implemented in any comparable or analogous storage system110 regardless of the manufacturer, product name, or components orcomponent names associated with the storage system 110. Any storagesystem 110 that could benefit from allocation techniques according tothe disclosure is deemed to fall within the scope of the disclosure.Thus, the enterprise storage system shown is presented only by way ofexample and is not intended to be limiting.

In selected embodiments, each server 206 includes one or more processors212 (e.g., n-way symmetric multiprocessors) and memory 214. The memory214 may include volatile memory (e.g., RAM) as well as non-volatilememory (e.g., ROM, EPROM, EEPROM, hard disks, flash memory, etc.). Thevolatile memory and non-volatile memory may store software modules thatrun on the processor(s) 212 and are used to access data in the storagedevices 204. The servers 206 may host at least one instance of thesesoftware modules. These software modules may manage all read and writerequests to logical volumes in the storage devices 204.

FIG. 3 is a flowchart illustrating an operation 300 processing an extendrequest according to an embodiment. Operation 300 may ensure data setsare more likely able to extend to additional volumes when required by anapplication. Operation 300 may work on a variety of operating systems.In embodiments, operation 300 may work on database management solutions.Operation 300 may begin at block 301. The extend request may be receivedat block 310. The extend request may be for a data set. The extendrequest may include a new extent allocation amount for the data set. Thedata set may be associated with a number of volumes in a storagefacility. The number of volumes may be a predetermined value or may beuser specified. The number of volumes may be constrained, for example,by a DVC.

At block 320, a decision may be made whether to spread the new extentallocation amount across multiple volumes. The decision of block 320 mayinclude determining to conduct normal allocation. Normal allocation maybe conducted at block 325 and the operation 300 may conclude at block399. The decision of block 320 may include determining to apportion thenew extent allocation amount among fractional amounts. In embodiments,SMS may proceed with a standard volume selection process for data setextend request processing. The standard volume selection process mayfail. Failure may occur because no single volume in a selected SGcontains enough free space to satisfy the extend request. Putdifferently, it may be determined that zero of the number of volumes canaccommodate the new extent allocation amount. A volume allocationthreshold may be associated with the number of volumes. The volumeallocation threshold may be a predetermined value or may be userspecified. The volume allocation threshold (allocation/migrationthreshold) of the selected SG may be altered. The alteration may bedynamic. For example, in an SMS environment Storage Groups may bedefined with the volume allocation threshold set to a default value of85%. In the example, if a request on a volume will cause the percent ofused space on the volume to exceed its threshold, the request as to thatvolume is rejected. The alteration may set the volume allocationthreshold to a higher value. The alteration may be user defined. Forexample, the volume allocation threshold may be altered so as to be setat 90%. The extend request may proceed again with the standard volumeselection process, just at a different volume allocation threshold.Failure may once again occur as it may be determined that still zero ofthe number of volumes can accommodate the new extent allocation amount.

Operation 300 may spread the new extent allocation amount acrossmultiple volumes. Spreading the new extent allocation amount acrossmultiple volumes may allow an extend request to succeed and not disruptapplications. The new extent allocation amount may be apportioned amongfractional amounts at block 330. The fractional amounts may include atleast a first fractional amount and at least a second fractional amount.More fractional amounts are considered (e.g., a third fractionalamount). The first fractional amount may be allocated to a first volumeat block 340. The second fractional amount may be allocated to a secondvolume at block 350. In embodiments, the fractional amounts may bedivided so that the fractional amounts are not too small or too large.In embodiments, the fractional amounts may be divided so that thefractional amounts are associated with free space in particular volumes.In embodiments, the new extent allocation amount may be apportionedamong fractional amounts and allocated to any plurality of volumes up tothe operating system limit (e.g., 59 for one particular databasemanagement solution).

In embodiments, the new extent allocation amount may be spread over (upto) a number of candidate volumes following failure occurring subsequentto altering the volume allocation. If no candidate volumes exist, andthe data set is defined with a DVC, the same methodology of spreadingthe new extent allocation amount across the DVC may be used. The numberof candidate volumes may be defined in the extending data sets catalogentry. In embodiments, the new extend allocation amount may be spread upto the number of volumes defined in the DVC of the data set in a DataClass. SMS may drive Direct Access Device Space Management (DADSM) tosatisfy the extend request up to the number of candidate volumes or DVC.Any candidate volumes not required to satisfy the extend request may beimmediately returned to a candidate status in the catalog entry.

Operation 300 may conclude at block 399. It may be determined that atleast one of the number of volumes can accommodate the new extentallocation amount. If spreading the new extent allocation amount acrossmultiple volumes succeeded, control may be passed back to theapplication and normal processing may continue. It may be determinedthat zero of the number of volumes can accommodate the new extentallocation amount. If spreading the new extent allocation amount acrossmultiple volumes failed, the extend request may be considered failed andappropriate error messages may be returned to the application.

In embodiments, a space management utility may key off an indicator or anew value. The new value may be a new bit. The new bit may be defined,for example, in the catalog entry for the data set. The new bit mayindicate which volumes were utilized to store fractional amounts byoperation 300. Thus, after allocating the new extent allocation amount,it may be determined that a third volume can accommodate the new extentallocation amount. The first and second fractional amounts may bereallocated to the third volume. The third volume may be a primaryvolume. Therefore, the space management utility may move data stored infractional amounts in the number of volumes by operation 300 to aprimary volume for a data set. The volumes utilized to store fractionalamounts by operation 300 may be returned to a candidate status in acatalog.

FIG. 4 shows modules of a system implementing operation 300 according toan embodiment. In embodiments, operation 300 may be implemented in theform of one or more modules. These modules may be implemented inhardware, software or firmware executable on hardware, or a combinationthereof. For example, module functionality may occur in a host system106 may actually be implemented in a storage system 110 and vice versa.Other functionality may be distributed across the host system 106 andthe storage system 110.

A host system 106 may include an extent allocation module 400. Theextent allocation module 400 may facilitate management of a storagesystem 110 hosting a data set 420 comprising a number of volumes 422adapted to have extents 424. The extent allocation module 400 mayinclude an extend request reception module 402, a new extent allocationamount module 404, an apportioning module 406, an allocating module 408,a number of volumes accommodation module 410, a volume allocationthreshold module 412, and a reallocation module 414.

The extend request reception module 402 may receive particular extendrequests which may be for data sets. The new extent allocation amountmodule 404 may be associated with the extend request reception module402 and may be represented as values received as part of particularextend requests. The apportioning module 406 may decide to spread thenew extent allocation amount across multiple volumes and may apportionnew extent allocation amounts among fractional amounts. The allocatingmodule 408 may allocate the fractional amounts to the number of volumes.The number of volumes accommodation module 410 may determine how many ofthe number of volumes can accommodate the new extent allocation amountsof particular extend requests. The volume allocation threshold module412 may alter the volume allocation threshold to attempt to satisfyparticular extend requests by standard volume selection processes. Thereallocation module 414 may use space management utilities to move datastored in fractional amounts in the number of volumes to primaryvolumes.

In addition to embodiments described above, other embodiments havingfewer operational steps, more operational steps, or differentoperational steps are contemplated. Also, some embodiments may performsome or all of the above operational steps in a different order. Themodules are listed illustratively according to an embodiment and are notmeant to indicate necessity of a particular module or exclusivity ofother potential modules.

In the foregoing, reference is made to various embodiments. It should beunderstood, however, that this disclosure is not limited to thespecifically described embodiments. Instead, any combination of thedescribed features and elements, whether related to differentembodiments or not, is contemplated to implement and practice thisdisclosure. Many modifications and variations may be apparent to thoseof ordinary skill in the art without departing from the scope and spiritof the described embodiments. Furthermore, although embodiments of thisdisclosure may achieve advantages over other possible solutions or overthe prior art, whether or not a particular advantage is achieved by agiven embodiment is not limiting of this disclosure. Thus, the describedaspects, features, embodiments, and advantages are merely illustrativeand are not considered elements or limitations of the appended claimsexcept where explicitly recited in a claim(s).

As will be appreciated by one skilled in the art, aspects of the presentdisclosure may be embodied as a system, method, or computer programproduct. Accordingly, aspects of the present disclosure may take theform of an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.), or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module,” or “system.”Furthermore, aspects of the present disclosure may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination thereof. More specificexamples (a non-exhaustive list) of the computer readable storage mediumwould include the following: an electrical connection having one or morewires, a portable computer diskette, a hard disk, a random access memory(RAM), a read-only memory (ROM), an erasable programmable read-onlymemory (EPROM or Flash memory), an optical fiber, a portable compactdisc read-only memory (CD-ROM), an optical storage device, a magneticstorage device, or any suitable combination thereof. In the context ofthis disclosure, a computer readable storage medium may be any tangiblemedium that can contain, or store, a program for use by or in connectionwith an instruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wire line, optical fiber cable, RF, etc., or any suitable combinationthereof.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including: an object oriented programminglanguage such as Java, Smalltalk, C++, or the like; and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute asspecifically described herein. In addition, the program code may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer, or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider).

Aspects of the present disclosure have been described with reference toflowchart illustrations, block diagrams, or both, of methods,apparatuses (systems), and computer program products according toembodiments of this disclosure. It will be understood that each block ofthe flowchart illustrations or block diagrams, and combinations ofblocks in the flowchart illustrations or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing the functionsor acts specified in the flowchart or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function or act specified in the flowchart or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus, or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions or acts specified in the flowchart or blockdiagram block or blocks.

Embodiments according to this disclosure may be provided to end-usersthrough a cloud-computing infrastructure. Cloud computing generallyrefers to the provision of scalable computing resources as a serviceover a network. More formally, cloud computing may be defined as acomputing capability that provides an abstraction between the computingresource and its underlying technical architecture (e.g., servers,storage, networks), enabling convenient, on-demand network access to ashared pool of configurable computing resources that can be rapidlyprovisioned and released with minimal management effort or serviceprovider interaction. Thus, cloud computing allows a user to accessvirtual computing resources (e.g., storage, data, applications, and evencomplete virtualized computing systems) in “the cloud,” without regardfor the underlying physical systems (or locations of those systems) usedto provide the computing resources.

Typically, cloud-computing resources are provided to a user on apay-per-use basis, where users are charged only for the computingresources actually used (e.g., an amount of storage space used by a useror a number of virtualized systems instantiated by the user). A user canaccess any of the resources that reside in the cloud at any time, andfrom anywhere across the Internet. In context of the present disclosure,a user may access applications or related data available in the cloud.For example, the nodes used to create a stream computing application maybe virtual machines hosted by a cloud service provider. Doing so allowsa user to access this information from any computing system attached toa network connected to the cloud (e.g., the Internet).

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams or flowchart illustration, andcombinations of blocks in the block diagrams or flowchart illustration,can be implemented by special purpose hardware-based systems thatperform the specified functions or acts, or combinations of specialpurpose hardware and computer instructions.

While the foregoing is directed to exemplary embodiments, other andfurther embodiments of the disclosure may be devised without departingfrom the basic scope thereof, and the scope thereof is determined by theclaims that follow.

What is claimed is:
 1. A computer program product comprising anon-transitory computer readable storage medium having programinstructions embodied therewith, the program instructions executable bya processor to cause the processor to perform a method comprising:receiving an extend request, the extend request including a new extentallocation amount for a data set, the data set associated with a numberof volumes in a storage facility, wherein the number of volumes includesat least a first volume, a second volume, and a third volume, wherein atleast one of the first volume and the second volume is associated with adynamic volume count (DVC) and is not a candidate volume of the dataset, wherein the third volume is not associated with the DVC and is aprimary volume or a candidate volume of the data set; increasing a totalpercentage of space of each volume which may be used for extentallocations; apportioning the new extent allocation amount amongfractional amounts, the fractional amounts including at least a firstfractional amount and at least a second fractional amount; allocatingthe first fractional amount to the first volume; allocating the secondfractional amount to the second volume; determining, after allocatingthe first and second fractional amounts, that the third volume canaccommodate the new extent allocation amount; and reallocating the firstand second fractional amounts to the third volume.
 2. The computerprogram product of claim 1, wherein the program instructions configuredto cause the processor to increase the total percentage of space of eachvolume which may be used for extent allocations are further configuredto cause the processor to perform a method further comprising:determining that zero of the number of volumes can accommodate the newextent allocation amount; and increasing, in response to determiningthat zero of the number of volumes can accommodate the new extentallocation amount, a volume allocation threshold, wherein the volumeallocation threshold is associated with the number of volumes andindicates the total percentage of space of each volume which may be usedfor extent allocations.
 3. The computer program product of claim 1,wherein the program instructions configured to cause the processor toapportion the new extent allocation amount among fractional amounts arefurther configured to cause the processor to perform a method furthercomprising: determining, in response to increasing the total percentageof space of each volume which may be used for extent allocations, thatzero of the number of volumes can accommodate the new extent allocationamount; and apportioning the new extent allocation amount amongfractional amounts.
 4. The computer program product of claim 1, whereinthe third volume and the first volume are the same volume.
 5. Thecomputer program product of claim 1, wherein the program instructionsconfigured to reallocate the first and second fractional amounts to thethird volume are further configured to cause the processor to perform amethod further comprising: allocating the first fractional amount to thethird volume; allocating the second fractional amount to the thirdvolume; deallocating the first fractional amount from the first volume;and deallocating the second fractional amount from the second volume. 6.The computer program product of claim 1, wherein the programinstructions configured to cause the processor to apportion the newextent allocation amount among fractional amounts are further configuredto cause the processor to perform a method further comprising:apportioning the new extent allocation amount among at least the firstfractional amount, at least the second fractional amount, and at least athird fractional amount; and allocating the third fractional amount tothe third volume.
 7. A computer program product comprising anon-transitory computer readable storage medium having programinstructions embodied therewith, the program instructions executable bya processor to cause the processor to perform a method comprising:receiving an extend request, the extend request including a new extentallocation amount for a data set, the data set associated with a numberof volumes in a storage facility, wherein the number of volumes includesat least a first volume, a second volume, and a third volume, wherein atleast one of the first volume and the second volume is associated with adynamic volume count (DVC) and is not a candidate volume of the dataset, wherein the third volume is not associated with the DVC and is aprimary volume or a candidate volume of the data set; determining thatzero of the number of volumes can accommodate the new extent allocationamount; increasing a volume allocation threshold, wherein the volumeallocation threshold indicates a total percentage of space of eachvolume which may be used for storage of data sets; determining, afterincreasing the volume allocation threshold, that no single volume of thenumber of volumes can accommodate the new extent allocation amount withthe increased volume allocation threshold; in response to determiningthat no single volume of the number of volumes can accommodate the newextent allocation amount with the increased volume allocation threshold,apportioning the new extent allocation amount among fractional amounts,the fractional amounts including at least a first fractional amount andat least a second fractional amount; allocating the first fractionalamount to the first volume; allocating the second fractional amount tothe second volume; determining, after allocating the first and secondfractional amounts, that the third volume can accommodate the new extentallocation amount; and reallocating the first and second fractionalamounts to the third volume.